CATEGORIES Report Summary

Final Report Summary - CATEGORIES (THE ORIGIN AND IMPACT OF COLOUR CATEGORIES IN THOUGHT AND LANGUAGE)

The grouping of objects, entities or sensations into categories provides essential structure for thought and language, enabling efficiency in how humans think and communicate. Understanding how humans categorise is therefore crucial for understanding the complexity of the human mind. When and how categories are formed? How do categories in language and thought relate? How are categories expressed in the brain?

The ‘CATEGORIES’ project is a five year European Research Council (ERC) funded project led by Professor Anna Franklin. The project uses colour categorisation as a testing ground for fundamental questions on how humans categorise perceptual information. Although the colour spectrum is continuous, discriminable colours are grouped into categories such as blue, green and red. How colour is grouped into categories varies across languages, for example many of the worlds languages have one basic colour term that includes both blue and green colours. This could suggest that languages arbitrarily divide up the colour spectrum into categories. However, there is also evidence to suggest that young infants also treat colour categorically (e.g., they know blues are the ‘same kind of colour’). The ‘CATEGORIES’ project aimed to understand how infants categorise colour in the absence of language and how these ‘pre-linguistic’ colour categories relate to those in the world’s colour lexicons. In addition, the project investigated whether speakers of different colour lexicons differ in how they ‘see’ colour, and how their colour categories are represented in the brain.

The ‘CATEGORIES’ team have made four key breakthroughs. First, testing of over 400 infants has revealed a ‘map’ of infant colour categories, with the colour spectrum being divided into the five categories of green, blue, red, yellow and purple. The infant category map corresponds closely to commonalities in the world’s colour lexicons. For example, the ‘fault lines’ that divide up the infant category map correspond to regions of the spectrum which are least likely to be good examples of colour terms across languages. The project found that infants use the retinogeniculate pathways responsible for early colour coding to categorise colours. This therefore provides clear that colour categories initially have a biological basis and represents a theoretical breakthrough for the field. Second, a series of psychophysical and electrophysiological experiments with adults has revealed that, when colour is attended, colour categories affect later but not early ‘sensory’ stages ofhow colours are seen. For example, experiments with Russian and English speakers who vary in their colour lexicons reveal cross-linguistic differences in colour processing from 220 ms after a colour is shown but not before this. Third, neuroimaging of adults’ brains whilst they view colours has identified the region of the brain which categorises colours. This region, the middle frontal gyrus, is involved in categorisation of other types of information, suggesting that colour is categorised using general attentional mechanisms that rely on a neural network common to other forms of categorisation. Fourth, the project investigates relationships between colour naming and other aspects of colour perception and cognition that have not previously been investigated. For example: i) the project finds that children’s colour term acquisition relates to their ability to keep colours perceptually constant under changes in illumination; ii) the project also finds that colours that are easy to name are more liked and demonstrates this for both people with normal colour vision and those with a colour vision deficiency; iii) the project finds that colour categories do not affect how we quickly get the gist of multi-coloured scenes. These findings go beyond prior work that has asked how colour terms affect our sensitivity to colour differences, to demonstrate the range of perceptual and cognitive phenomenon that are affected by how we talk about colour.